This invention relates generally to surgically implanted physiological shunt systems and related flow control devices. More particularly, the present invention relates to shunt systems including one-way flow control valves for controlling the flow of cerebrospinal fluid out of a brain ventricle and preventing backflow of fluid into the brain ventricle.
In the medical arts, to relieve undesirable accumulation of fluids it is frequently necessary to provide a means for draining a fluid from one part of the human body to another in a controlled manner. This is required, for example, in the treatment of hydrocephalus, a ailment usually afflicting infants or children in which fluids accumulate within the skull and exert extreme pressure and skull deforming forces.
In treating hydrocephalus, cerebrospinal fluid accumulated in the brain ventricles is typically drained away utilizing a drainage or shunt system including a catheter inserted into the ventricle through the skull, which is connected to a tube which conducts the fluid away from the brain to be reintroduced into the peritoneal cavity or into the vascular system, as by extending a distal catheter through the patient's jugular vein to the atrium portion of the heart. To control the flow of cerebrospinal fluid and maintain the proper pressure in the brain ventricle, a pump or valve is placed in the conduit between the brain and the peritoneal cavity or the heart. An exemplary flow control device is found in U.S. Pat. No. 4,560,375.
Although such drainage systems have provided successful results, a problem of over drainage of the cerebrospinal fluid from the brain ventricles sometimes exists. Over drainage of cerebrospinal fluid may result in excessive reduction of the cerebrospinal fluid pressure within the brain ventricles and predispose the development of a subdural hematoma or hydroma, and excessive reduction of ventricular size leading to shunt obstruction because of impingement of the ventricular walls on the inlet holes of the ventricular catheter. This over drainage can be caused by the siphoning effect of hydrostatic pressure in the distal shunt catheter. The siphoning effect of hydrostatic pressure may be created by the elevation of the ventricular catheter inlet with respect to the distal catheter outlet (i.e., when the patient sits, stands or is held erect). In order to prevent such over drainage caused by the siphoning effect of hydrostatic pressure in the distal shunt catheter, siphon control devices have been placed in the conduit, typically between the flow control device and the peritoneal cavity or the heart. An exemplary siphon control device is found in U.S. Pat. No. 4,795,437.
It is desirable in some instances to permit the physician to be able to alter the flow characteristics through the drainage system after it has been subcutaneously implanted. To this end, on-off devices have been provided for implantation as a portion of the fluid conduit, as an additional element of the shunt. An exemplary on-off device is shown in U.S. Pat. No. 3,827,439.
Prior physiological shunt systems have failed to provide, however, a flow control device which permits only unidirectional flow through the shunt system, prevents over drainage caused by the siphoning effect of hydrostatic pressure in the distal shunt catheter, and permits the flow characteristics through the shunt to be altered by means of percutaneous pressure after the shunt system has been surgically implanted. Further, existing flow control devices extensively used in connection with the treatment of hydrocephalus typically provide only a single pre-set resistance to the flow of excess cerebrospinal fluid through the shunt system, which cannot be varied except to prevent fluid flow through the shunt by means of an on-off valve.
Accordingly, there has been a continuing need in the medical arts for convenient and effective physiological drainage devices for controlling the flow of fluid from one part of the body to another, which are relatively inexpensive to manufacture and can be constructed substantially of non-metallic parts which are not subject to adhering to one another and causing a malfunction of the device. A flow control device is needed which permits fluid flow therethrough only when upstream fluid pressure exceeds downstream fluid pressure by a selected pressure differential, and which also provides means for altering the selected pressure differential by manual percutaneous manipulation of the device when it is subcutaneously implanted.
Additionally, a novel flow control device for use in a physiological shunt system is needed which utilizes a plurality of flow control valves having different flow control characteristics. Such a device should provide alternative fluid pathways therethrough such that selection of the desired fluid pathway can be made by the selective application of percutaneous manual pressure to the device when it is subcutaneously implanted. Moreover, such a flow control device is needed which incorporates an integral siphon control device that opens only in response to positive upstream fluid pressure, and recloses or remains closed in the absence of such positive upstream fluid pressure or in response to negative downstream hydrostatic pressure on the device. As will become apparent from the following description, the present invention satisfies these needs and provides other related advantages.